BEIRUT — Syria's main opposition alliance on Wednesday urged fighters from around the country to reinforce a rebel-held town under attack by President Bashar Assad's troops and their allies from the Lebanese militant Hezbollah group.

With its appeal, the Syrian National Coalition sought to bolster embattled rebel forces in Qusair who for a fourth straight day Wednesday came under fierce assault by government troops.

The town, which is near the border with Lebanon, lies at the heart of a government offensive to secure a strategic strip running from the capital, Damascus, to the Mediterranean coast and Syria's seaports.

The Iranian-backed Hezbollah group has been fighting alongside Syrian regime forces in the town and surrounding areas in Homs province for weeks. Hezbollah has been trying to keep a low profile, but could no longer do so after several dozen of its fighters were killed in the battle over Qusair.

U.S. Secretary of State John Kerry, speaking in neighboring Jordan, called on Iran and Hezbollah to stop helping Assad, saying this activity "perpetuates the regime's campaign of terror against its own people."

Underlining the importance of Qusair, George Sabra, head of the main political opposition group, the Syrian National Coalition, on Wednesday urged rebels from all over Syria to join the fight for the town.

Opposition fighters in Qusair were holding out Wednesday, but appeared to be under increasing strain as government tanks and artillery pounded the town and warplanes bombed it from the sky.

A local government official from the Homs governor's office told The Associated Press that about 80 percent of Qusair was in government hands. The official spoke on condition of anonymity because he was not allowed to give information to the media during an ongoing military operation.

He added that Assad's troops discovered tunnels linking areas around the town, and that the fighting is now concentrated in the northwestern parts of Qusair where the "terrorists" – the phrase regime uses for opposition fighters – were still entrenched. The official's account could not be independently verified because Damascus bans independent media access to much of the country.

Rami Abdul-Rahman, who heads the Britain-based Syrian Observatory for Human Rights activist group, said Syrian government and Hezbollah units were bombarding Qusair with rockets on Wednesday.

The Observatory said at least 31 Hezbollah fighters have been killed in the battle for Qusair since Sunday. The group, which relies on a wide network of activists on the ground in Syria, said at least 83 rebels and nine Syrian soldiers were also killed, as well as six Lebanese fighting on the rebel side.

A video released by activists on Tuesday showed destruction in several areas in the city as well as heavy damage to the minaret of Qusair's grand mosque that was riddled with bullets and shells.

The video appeared genuine and corresponded to other AP reporting on the events depicted.

Hezbollah's role in the fighting in Qusair has ratcheted up tensions in neighboring Lebanon, which has been on edge since the Syrian conflict began in 2011. Lebanon and Syria share a complex web of political and sectarian ties and rivalries that are easily enflamed.

Most of Lebanon's Sunni Muslims back the Syria's predominantly Sunni opposition, while Shiites support the Assad regime, which is dominated by members of his minority Alawite sect, an off-shoot of Shiite Islam.

More than 70,000 people have been killed and several million displaced by the conflict that erupted more than two years ago.

Fighting raged Wednesday in the northern Lebanese city of Tripoli between supporters and opponents of Assad. Lebanese security officials said that at least 10 people, including two Lebanese soldiers, have been killed and more than 100 wounded since Sunday in Tripoli. The officials spoke on condition of anonymity in line with regulations.

Also Wednesday, the U.N. agency aiding Palestinian refugees across the Middle East said between 70 percent to 80 percent of the half million Palestinian refugees in Syria were uprooted over the past two years.

Despite the fighting, the international community hopes to bring representatives of the regime and the opposition to an international conference in June to launch peace talks. The goal is to form a joint transitional government to pave the way for elections, but gaps between the sides remain wide.

Kerry told reporters in Amman on Wednesday that the United States and its Arab and European allies will step up their support for Syria's opposition to help them "fight for the freedom of their country" if Assad does not engage in peace talks in good faith.

The U.S. has been unwilling to send weapons to the rebels. Kerry did not explain how additional non-lethal support to rebel fighters would help them reverse a string of recent military successes by the regime. Russia and Iran have continued to supply weapons to Syria throughout the conflict, while Hezbollah has sent thousands of fighters to Syria to support Assad.

In Germany, the weekly Der Spiegel reported that the German intelligence chief has revised his assessment of the Syrian civil war.

The chief, Gerhard Schindler, told a small group of politicians dealing with security issues in a secret briefing that Assad's military is stronger than it has been in a long time, according to Der Spiegel. Additional successful offensives of the regime are possible anytime, he said.

The German intelligence agency BND believes this is a turning point. At the end of 2012, it appeared the regime was in its end phase.

He said the channels for restocking the regime's weapons supplies are now open, and the supply of gas for tanks and aircraft is also working again. Schindler said Assad most likely won't be able to defeat the rebels, but he can contain them and even win back some territory.

The BND predicts that in 2013, regime troops will be able to recapture additional territory. If the fighting continues as it has in recent weeks, the regime could recapture the entire south by the end of the year. In this case, the rebels would be left with only the north.

On Wednesday, Germany's Foreign Ministry said it supports adding Hezbollah to the EU's list of terrorist groups. The ministry linked the recommendation to a deadly attack on Israeli tourists in Bulgaria last year that was tied to Hezbollah.

Sylke Tempel, a Mideast expert at the German Council on Foreign Relations in Berlin, said she believed the German support for sanctions against Hezbollah's military wing was due in part to its role in Syria fighting.

She said the presence of Hezbollah fighters in Syria has led Western and regional governments to ponder "what if Assad is going to win this thing" and "what if Hezbollah is a factor in making Assad win, or at least not lose."

___

Associated Press writers Robert H. Reid in Berlin and Albert Aji in Damascus, Syria contributed to this report.